TUESDAY, Feb. 27, 2018 (HealthDay News) -- Those tangled blue varicose veins that can pop up on your legs as you age may be more than unsightly: New research suggests they might quintuple your risk of dangerous blood clots.

Known as deep venous thrombosis (DVT), these clots in the legs can be life-threatening if they travel to the lungs or heart, Taiwanese researchers said.

"Varicose veins are not merely a cosmetic or symptomatic concern, because they may be associated with increasing risk of more serious disease," explained lead researcher Dr. Shyue-Luen Chang, a phlebologist in the department of dermatology at Chang Gung Memorial Hospital in Taoyuan.

Varicose veins are a common condition affecting about 23 percent of American adults, the researchers said.

"Patients with varicose veins may warrant careful monitoring and early evaluation," Chang added.

Among a group of more than 425,000 people, half of whom had varicose veins, Chang's team found that the condition was associated with 5.3 times increased risk of deep venous thrombosis.

Whether varicose veins cause the clots, or are a real risk for them, however, is not known, Chang said. More research is needed since the study did not prove that varicose veins cause the clots, he said.

"Not much is known about varicose veins and the risk for these other diseases," Chang said. "Elucidating potential associations between varicose veins and health-threatening diseases is important."

The researchers also found a trend for an increased risk of pulmonary embolisms or PE (clots in the lung) or PAD (narrowing of the leg arteries) among those with varicose veins, but they weren't able to tell if varicose veins were a real risk for these conditions.

For the study, Chang and colleagues used data from Taiwan's National Health Insurance program. Patients were enrolled in the database from 2001 to 2013, and they were followed through 2014.

One weakness of the study is that insurance claims data do not include information on patients who don't seek medical care.

Therefore, the findings may apply only to risk among patients with more severe varicose veins who needed medical attention, the researchers explained.

One U.S. cardiologist called for more research on the possible connection.

"Given the very high prevalence of varicose veins in the general population worldwide, the results of this trial should trigger future studies to further investigate the effect of varicose veins on the inflammation and formation of a blood clot, and to assess the link between the severity of varicose veins and DVT," said Dr. Maja Zaric. She's an interventional cardiologist at Lenox Hill Hospital in New York City.

The study suggests that varicose veins should be taken more seriously and likely treated more aggressively, she said.

"It is prudent to establish which category of patients with varicose veins is at the greatest risk and how aggressive and early the treatment should be to prevent serious complications, given morbidity and mortality associated with both DVT and PE," Zaric said.

The report was published Feb. 27 in the Journal of the American Medical Association.